Light-sensitive layers for graphic arts purposes using polyvinyl benzyl n-(4-vinylpyridinium) salts



United States Patent Int. (:1. G03c1/70, 5/00 U.S. Cl. 96-115 5 Claims ABSTRACT OF THE DISCLOSURE Light-sensitive material having, on a support, a layer of a polymer susceptible to cross linking whereby it becomes insolubilized when exposed to light, and a photosensitizer therefor, the polymer containing in its structure at least mol percent of a polymerizable vinylbenzy1-N-(4-vinyl)-pyridine quaternary salt wherein the 4-vinyl group has an aryl, thienyl or furyl group in fi-position, or a vinylene homolog of such salt.

It is known to employ different polymers as light-sensitive systems. Exposed as a thin layer on a suitable sup port through an original they are crosslinked imagewise, i.e., hardened locally so that a following development with a solvent or solvent mixture for the polymer redissolves the not-crosslinked layer areas, whereas crosslinked areas have become insoluble by the exposure. Such systems with inherent layer sensitivity which are operative without additional inductors of photocrosslinking such as dichromates or diazides, which are added to water-soluble polymers or natural products such as polyvinyl alcohol, gelatin, albumen, and also to organophilic materials such as cyclized caoutchouc or butadiene-styrene copolymers, are known, Among them are cinnamic acid esters of polyvinyl alcohol, including those with a urethane linkage, also chalcones linked to polymers in the same manner.

It is also known to prepare polymers containing azide groups which possess inherent sensitivity to light and UV radiation. Such compounds and copying layers made with them have been described, for example, in German Patents 1,053,782, 1,079,949 and 1,114,704. The latter includes the use of diazo compounds.

A disadvantage of the systems named is the low resistance of the crosslinked layers against strong acids which are used to etch the processed plates. Other drawbacks are frequently the low sensitivity of the layers, and the processing of the light-sensitive materials caused, e.g., by the poor adhesion of the layers to the support.

Some time ago (Makromol. Chem. 73, 203-214; 1963) poly-(2-ary1vinyl-N-vinylpyridinium arylsulfonates) were described as new class of photocrosslinkable polymers. The paper cited describes the preparation and photocrosslinking of compounds of the structure 3,462,274 Patented Aug. 19, 1969 "ice It has now been found that photocrosslinkable layers with excellent properties can be obtained if the light-sensitive polymers consist wholly or in part of polymerized units or salts of vinylbenzyl-N-( l-vinyl)-pyridine whose vinyl group is substituted in fi-position with an aromatic ring, or of the vinylene homologs of such units, i.e., units in 'which the fl-substituted 4-vinyl group is replaced by the radicle C- -CH'CH=CH% wherein m is an integer, and the terminal carbon atom C= is joined to at least one aromatic ring. Particularly suitable are polymers with units of the following structure:

wherein R is an aromatic (aryl or quasiaromatic heterocyclic) residue, e.g., phenyl, naphthyl, thienyl, or furyl. These aromatic rings, as well as the phenylene ring of the benzyl group or the pyridine ring may contain further substituents, especially halogen such as C1 or Br, alkyl with preferably up to 5 carbon atoms, alkoxyl also With preferably up to 5 carbon atoms, N0 nitrile, phenyl, naphthyl, and the like. The selected substituents must not interfere with the photocrosslinking properties; certain properties, e.g., the solubility, can be influenced favorably by suitable substituents; n represents a whole number between 1 and 5, preferably 1 or 2, especially 1; and A represents any anion. The type of anion is not critical, and depends on the method of preparation. Generally it will be a halogen anion such as Cl, 80;: tosylate, alkylsulfonate anions or the like.

The polymers of the invention containing the above units preferably have a molecular weight between 1000 and 15,000. Preferred are products containing at least 10 mole percent of units of the above general structure. The polymers may contain any other polymerizable vinyl compounds in polymerized form. Certain properties of the polymers, e.g., the solubility, can thereby be adjusted in a desired manner. Suitable copolymer components are, for example, styrene, ethylene, propylene, butylene; acrylic acid, methacrylic acid, or their derivatives (e.g., esters, amides or nitriles); vinyl esters (e.g., vinyl acetate); vinyl ethers (e.g., vinyl butyl ether); vinyl chloride, or mixtures thereof.

Layers made with the compounds of the invention exhabit good film forming properties can be prepared simply and in good yield, and have high speeds. Crosslinked layers exhibit a good resistivity against etching chemicals such as nitric acid and are therefore excellently suited for the preparation of etch resists for various purposes. The novel compounds can also be made with other than the mentioned starting polymers, especially copolymers of polystyrene with acrylonitrile, acrylic esters, N-vinylpyrrolidone, or N-vinyl carbazole. Light-sensitive layers of the invention can be sensitized in the conventional manner, particularly by compounds containing ketone or aldehyde functions, e.g., 4,4-dimethyla minobenzophenone (Michlers ketone) and 4-aminobenzaldehyde.

It is technically very desirable that the absorption of this compound extends into the relatively long wavelengths (up to about 500 m because of the positive charge of the N in a conjugated system, and therefore it is far more favorable for light sources emitting in the visible range than, e.g., polyvinylcinnamate. However, the compounds are hygroscopic, and form unsatisfactory films with poor adhesion, so that photocrosslinking did not produce the desired results.

Suitable as supports for the novel layers are particularly metals such as Zn, Al, Mg, Cu, Fe as well as others which suit the purpose in question. All light sources suitable for such purposes can be used for the crosslinking if they have the proper intensity in the visible and UV regions, e.g. carbon arc lamps, xenon high pressure arcs, Hg vapor lamps, etc. as well as sunlight. Preferred is the use of carbon arcs, xenon lamps, and Hg high pressure lamps.

3 4 For better evaluation of the results achieved the layers of uncrosslinked layer components, and which adheres of the invention can be stained after the crosslinking, e.g. well to the support. On etching for 5 minutes in 5% nitric with a solution of crystal violet in chloroform. acid, rinsing and drying, a metal relief is obtained which Suitable polymers contain units of the following types: is suitable for use as a printing matrix.

-oHgdH--oHi-N: CH=OH- Cl- II F -oH.-oH-C -om-iq OH=CHOCH3 01- III The compounds are prepared by quaternizing poly E l 2 (vinyl benzyl chloride) with picoline and further condensation with suitable aromatic or quasiaromatic aldehydes, e.g. benzaldehyde, methoxybenzaldehyde, furfurol, cinnamaldehyde, or naphthaldehyde.

The preparation of some compounds is described as follows:

(1) Poly (vinyl benzyl mixture of 275 0nd brief development (1 mm.) with fresh developer in g Stannic chloride and 37 m1 monochlorodimethyl ethm. order to be certain to remove unexposed layer residues. are added dropwise with stirring to a mixture of 37 g.

The process of Example 1 is repeated, but as support, a plate of a phenol-formaldehyde resin covered with copper foil is used. After exposure and development, a relief is obtained as in Example 1. If layers thicker than that of Example 1 are applied, it is advisable to carry out a secpolystyrene (mol. wt. 1000-1500) with 37 ml. mon0- Exalmli'1e 3 chlorodimethyl ether, and the mixture then heated with 20. g. of the compound of Formula IV are dissolved stirring for 6 hours at Purification is achieved y at 40 c. in 200 ml. chloroform, and a solution of 0.4 g.

solution. Yield 40 g. added. The resulting solution is coated as in Example 1 (2) Quaternization with picoline.A solution of 18.6 40 and the dried coating exposed in the same manner, but for g. 4-picoline in 30 ml. dioxane is added dropwise to a 30 seconds only. After development in chloroform for 20- solution of 60 g. poly (vinyl benzyl chloride) in 400 ml- 30 seconds, sharp-edged reliefs with especially smooth dioxane, and the mixture stirred for 1 hour at room temsurface are produced. Some drops of 33% nitric acid apperature and then 5 hours at 50 C. After evaporation of plied after drying cause no observable change of the layer. the dioxane in vacuo, the resulting readily Water-soluble quaternary salt is digested again with acetone and dried Example 4 over P 0 in vacuo.

(3) Compound I.--10.5 g. of the above quaternary salt is stirred in the dark with 3-4 times its weight of benzaldehyde and 1.74 ml. piperidine for 140 hours at 45 C. The condensation product is precipitated by adding about 1 liter of acetone, filtered out, and dried over P 0 The other compounds listed in the table can be prepared analogously. The chloromethylation and following quaternization can be applied to copolymers which may be prepared as follows:

A mixture of 45 ml. styrene and 5 ml. ethyl acrylate (or 47.5 ml. styrene and 2.5 ml. acrylonitrile) is added dropwise at 7080 C. to a solution of 0.6 ml. SnCl in 25 ml. benzene, and the mixture stirred for 4 hours at 75 C. The resulting polymers are precipitated by adding methanol. For purification they are dissolved in chloroform and reprecipitated by addition of methanol.

The process of Example 3 is repeated, but the 4-(dimethylamino)-benzaldehyde is replaced by 1.0 g. Michlers ketone. After coating, exposure, and development the same result is obtained as in Eaxmple 3.

We claim:

1. Light-sensitive material having a support, and a layer thereon of a polymer susceptible to crosslinking under the influence of light whereby it becomes insoluble, and a photosensitizer therefor, said polymer comprising in its structure at least 10 mol. percent of polymerizable units selected from the group consisting of vinylbenzyl- N-(4-vinyl)pyridine quaternary salts wherein the 4-vinyl group is substituted in fi-position by a residue selected from the group consisting of aryl, thienyl and furyl residues, and the vinylene homologs of said salts.

2. Light-sensitive material according to claim 1, wherein said polymerizable units have the following formula: Example 1 48. g. of compound I prepared as described is dissolved at 40 C. in a mixture of 320 ml. chloroform and 80 ml.

ethanol. 1.8 g. Michlers ketone in 20 ml. chloroform is K added. The mixture is coated onto a well cleaned Zn plate to a layer of about 10 and dried for about 30 min. at 1 l Tepfecipitating the Product with methanol from benzene 4-(dimethylamino)-benzaldehyde in 10 ml. chloroform is room temperature. Then it is exposed through a line original for 1 minute to a carbon arc lamp (45 v. 15 amp),

at a distance of 30 cm., and developed for 2 min. in the wherein R is selected from the group consisting of aryl, solvent used for the coating. When dried, there remains thienyl and furyl residues, A is an anion, and n is a whole a sharp-edged relief whose background is clean and free number between 1 and 5.

3. Light-sensitive material according to claim 1, 'Wherein said polymerizable units have the following formula:

wherein R is an aryl radical and A- is an anion.

4. Light-sensitive material according to claim 1, where- 1 5. Light-sensitive material according to claim 1, wherein said photosensitizer is selected from the group consisting of aldehydes and ketones.

References Cited UNITED STATES PATENTS 10/ 1957 Robertson et a1 96-35 .1 10/1957 Leubner et al. 961l5 XR 10/ 1959 Williams 96-115 XR NORMAN G. T ORCHIN, Primary Examiner R. H. SMITH, Assistant Examiner US. Cl. X.R. 

